Combination oil ring

ABSTRACT

In mounting a combined oil control ring in a ring groove formed in a piston, the combined oil control ring is mounted in a form that an opening between but ends of an oil ring body is widened. In such an operation, it is likely that a coil expander falls off the oil ring body thus making the mounting operation cumbersome. To overcome such a drawback, a relationship L 1 &lt;L 2  is established. Here L 1  means a axial distance between open peripheries of the groove portion and L 2  means a maximum axial distance between peripheries of the groove portion.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a combined oil control ring which ismounted on a piston of an internal combustion engine.

2. Description of the Related Art

A combined oil control ring having an approximately M-shaped crosssection, which is configured such that upper and lower rails which bringouter peripheral surfaces thereof into slide contact with an innersurface of a cylinder and a web which connects the upper and lower railsand has a plurality of windows are integrally formed, is described inJapanese Unexamined Patent Publication Sho 61(1986)-45172 and JapaneseUnexamined Patent Publication Hei 9(1997)-144881, for example.

As shown in FIG. 4, the combined oil control ring consists of an oilring body 1 and a coil expander 2. The oil ring body 1 is an oil ringhaving an approximately M-shaped cross section in the radial directionwhich is formed of upper and lower rails 3, 4 and a web 5 which connectsthese rails 3, 4. Such a combined oil control ring is mounted in an oilring groove 21 formed in a piston 20.

Outer-peripheral protruding portions 6, 7 of the respective upper andlower rails 3, 4 have an approximately trapezoidal shape which is formedof outerperipheral slide surfaces 8, 9 which are brought into contactwith a cylinder wall 22 and upper and lower inclined surfaces 10, 11which are contiguous with the outer peripheral slide surfaces 8, 9. Sidesurfaces 12, 13 of the respective upper and lower rails 3, 4 facerespective upper and lower surfaces 23, 24 of the ring groove of thepiston.

In the combined oil control ring, a lubricant which is scraped by theslide surfaces 8, 9 of the rails is allowed to move into an innerperipheral side of the oil ring body 1 from an outer peripheral groove14 defined by the upper and lower rails 3, 4 and the web 5 through alarge number of windows 25 formed in the web 5. The lubricant which ismoved into an inner peripheral side of the oil ring groove 21 throughthe windows 25 is returned to an oil pan through an oil hole formed inthe piston 20.

As shown in FIG. 4, inner peripheral surfaces 18, 19 of inner-peripheralprotruding portions 15, 16 of the upper and lower rails 3, 4 have anarcuate shape and an inner peripheral groove 17 is formed of theinner-peripheral protruding portions 15, 16 and the web 5. The coilexpander 2 is housed in the inner peripheral groove 17. By bringing thecoil expander 2 and the arcuate surfaces 18, 19 of the inner peripheralgroove 17 of the oil ring body 1 into contact with each other, the oilring body 1 is pushed toward the cylinder wall 22.

The shape of the inner-peripheral protruding portions 15, 16 of theupper and lower rails 3, 4 may have a cross section of an approximatelytrapezoidal shape. In this case, as shown in FIG. 5, the innerperipheral groove 17 is formed of the inner-peripheral protrudingportions 15, 16 and the web 5. The coil expander 2 is housed in theinner peripheral groove 17. By bringing the coil expander 2 and taperedsurfaces 18, 19 of the inner peripheral groove 17 formed in the oil ringbody 1 into contact with each other, the oil ring body 1 is pushedtoward to the cylinder wall 22.

Here, as can be easily understood from FIG. 4 and FIG. 5, a maximumdistance L2 in the axial direction between the inner-peripheral-groovearcuate surfaces 18, 19 or the inner-peripheral-groove tapered surfaces18, 19 (see FIG. 5) of the oil ring body 1 is determined by a axialdistance between inner peripheries 27′, 28′ of the inner peripheralgroove 17.

As shown in FIG. 4, when the combined oil control ring, which the coilexpander 2 is housed in the oil ring body 1, is mounted in the oil ringgroove 21 of the piston 20, an opening between butt ends of the oil ringbody 1 is widened until an inner diameter of the combined oil controlring becomes larger than a piston diameter. However, when the openingbetween the but ends of the oil ring body 1 is widened, it is likely tooccur that the coil expander 2 falls off the inner periphery groove ofthe oil ring body 1. When the coil expander 2 falls off the innerperiphery groove of the oil ring body 1, it is necessary to restart theassembling operation of the coil expander 2 and the oil ring body 1 fromthe beginning.

Recently, in addition to enhance the conformability to the cylinderwall, the wear resistance and the scuff resistance of the combined oilcontrol ring, a demand for lowering tension of the coil expander isincreasing. By lowering the tension of the coil expander, it is possibleto obtain the excellent oil ring characteristics. On the other hand, thedrawback that the coil expander falls off the oil ring body duringassembling of the oil control ring to the piston becomes apparent.However, with respect to the combined oil control ring, nocountermeasures have been taken to prevent the coil expander fromfalling off heretofore.

SUMMARY OF THE INVENTION

The present invention has been made in view of the above-mentionedcircumstances and it is an object of the present invention to provide acombined oil control ring which can prevent a coil expander from fallingoff an oil ring body at the time of mounting the combined oil controlring on the piston without losing functions of the oil ring such as oilscraping.

To achieve the above-mentioned object, the present invention provides acombined oil control ring which consists of an oil ring body which isformed of upper and lower rails which bring outer peripheral surfacesthereof into slide contact with an inner surface of a cylinder and a web5 which connects the upper and lower rails and includes a plurality ofwindows, and a coil expander which pushes the oil ring body in thedirection toward the inner surface of the cylinder, the coil expanderbeing housed in an inner-peripheral groove of the oil ring body, whereinprojecting portions which extend toward a center line in the thicknessdirection are formed at inner peripheral sides in the radial directionthan a position where an axial distance between inner peripheries of aninner-peripheral groove portion of the oil ring body becomes maximum.Due to such a construction, when the oil control ring is mounted on thepiston by widening an opening between but ends of the oil ringbody, itis possible to prevent the coil expander housed in from falling off theoil ring body.

Further, at the time of mounting the combined oil control ring on thepiston, it is possible to prevent the coil expander from falling off bysetting an axial distance between the inner peripheries of theinner-peripheral groove portion of the oil ring body smaller than themaximum distance L2, in the inner portion than the position of L2.

It is preferable that L1 and L2 satisfy a relationship of0.03≦(L2−L1)/L1≦0.15. Here L1 means the minimum distance and L2 meansthe maximum distance. It is more desirable that L1 and L2 satisfy arelationship of 0.05≦(L2−L1)/L1≦0.10. When (L2−L1)/L1 is smaller than0.03, the remarkable falling-off prevention effect of coil expandercannot be recognized, while when (L2−L1)/L1 exceeds 0.15, it becomesdifficult to insert the coil expander into the oil ring body.

Further, according to the present invention, it is preferable that acoil diameter d of the coil expander and L1 of the oil ring body satisfya relationship of 0.2 mm ≧L1−d≧−0.10 mm. So long as this relationship issatisfied, there is no possibility that the oil ring body leaves thedeformation strain due to a force which is applied at the time ofopening the inner peripheral ends of the oil ring in the axial directionin housing the coil expander in the oil ring body. Further, when anopening between the but ends of the oil ring body is widened in theperipheral direction at the time of mounting the oil ring on the piston,the coil expander hardly falls off the oil ring body.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view in the radial direction of a combinedoil control ring showing one embodiment of the present invention;

FIG. 2 is a cross-sectional view in the radial direction of a combinedoil control ring showing another embodiment of the present invention;

FIG. 3 is a cross-sectional view in the radial direction of a combinedoil control ring showing another embodiment of the present invention;

FIG. 4 is a cross-sectional view in the radial direction of an exampleof a conventional combined oil control ring; and

FIG. 5 is a cross-sectional view in the radial direction of anotherexample of the conventional combined oil control ring.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments of the present invention are described in detailin conjunction with FIG. 1 to FIG. 3. With respect to constructions ofthese embodiments, the explanation of portions which are common with theportions of the prior art shown in FIG. 4 and FIG. 5 is omitted. Here,to some among the portions common with the portions shown in FIG. 4 andFIG. 5, the reference numerals used in FIG. 4 and FIG. 5 are given.

In the embodiment shown in FIG. 1, a thickness of the oil ring body 1 isset as L3 and the inner peripheral portions 18, 19 of theinner-peripheral protruding portions 15, 16 of the upper and lower rails3, 4 have an arcuate shape thus forming an inner-peripheral grooveportion 26 which houses the coil expander 2. With respect to theinner-peripheral groove portion 26, a width (distance) thereof in theaxial direction expands while drawing arcs toward the radially inwarddirection in a vertical symmetry (an upper and lower symmetry) from acrossing point A1 of the inner-peripheral groove portion 26 and athickness-direction center line (a line which passes the center of thewidth of the oil ring body 1) AA′ and assumes a maximum value L2 at aline BB′. Projecting portions 27, 28 which extend toward thethickness-direction center line AA′ are formed at positions disposedmore inside in the radial direction than the line BB′. Due to theprovision of these projecting portions 27, 28, it is possible to preventthe coil expander 2 from falling off at the time of mounting thecombined oil control ring on the piston 20.

In FIG. 1, the projecting portions 27, 28 are formed on open peripheriesof the inner-peripheral groove portion 26 and a distance between theopen peripheries in the axial direction assumes a minimum value L1 ininner position in the radial direction than the line BB′. However,provided that the projecting portion is formed in inner position thanthe line BB′, the position where the projecting portions are formed anddefine the minimum value L1 is not limited to the open peripheries.

Assume the distance in the axial direction between B, an upper end ofthe maximum axial distance L2 and a lower end of the upper projectingportion 27 as ΔL1, and the distance in the axial direction between B′, alower end of the maximum axial distance L2 and an upper end of the lowerprojecting portion 28 as ΔL2. In the construction shown in FIG. 1, theprojecting portions 27, 28 are formed in a vertical symmetry in theinner-peripheral groove portion 26 of the oil ring body 1 and ΔL1 andΔL2 are set equal.

Further, in the embodiment shown in the drawing, although the projectingportions 27, 28 have an approximately triangular cross section, theshape of the projecting portions 27, 28 is not specifically limited.Further, although the peripheral ends of the projecting portions 27, 28form an acute angle or are pointed, flattened portions may be formed onthe ends of the projecting portions 27, 28 or the ends of the projectingportions 27, 28 may be rounded in view of manufacturing reasons and theprevention of fracture.

Although the projecting portions 27, 28 maybe formed on the wholeperiphery of the oil ring body 1, it is possible to prevent the coilexpander from falling off even when the projecting portions 27, 28 areformed partially on the oil ring body in a circumferential direction.However, when the projecting portions 27, 28 are formed partially, it isnecessary to take proper measures to suppress the occurrence ofnon-uniform face pressure of the oil ring.

In an embodiment shown in FIG. 2, the inner-peripheral groove portion 26is formed of upper and lower inclined surfaces 18, 19 and a verticalsurface 30 which connects these inclined surfaces 18, 19. Further, bothof the upper and lower groove portions form arcuate surfaces from aposition slightly outside the line BB′ along which the width of theinner-peripheral groove portion 26 assumes the maximum in the axialdirection. Further, both of the upper and lower groove portions alsoform arcuate surfaces inside the line BB′ independently from the arcuatesurfaces outside the line BB′. In the same manner as the embodimentshown in FIG. 1, the projecting portions 27, 28 having a cross sectionof an approximately triangular shape are formed on open peripheries. Theoil ring body 1 having such a construction is also provided with theprojecting portions 27, 28 and the position which sets the minimum sizeL1 in the axial direction of the inner-peripheral groove portion 26 isnot always set at the open peripheries.

Further, it is not always necessary to form the arcuate surfaces formedin FIG. 2 and the inner-peripheral groove portion 26 may adopt theconfiguration in which the projecting portions 27, 28 maybe directlyformed next to inclined surfaces 18, 19. However, to prevent the coilexpander from falling off without causing any troubles in operation atthe time of mounting the coil expander 2, it is preferable that theprojecting portions 27, 28 are formed more gently and hence, it isdesirable to form the arcuate surfaces as shown in FIG. 2.

The construction shown in FIG. 3 is substantially equal to that of theembodiment shown in FIG. 1 except for a point that the projectingportion 28 is formed only on the lower portion and is not formed on theupper portion of the inner-peripheral groove portion 26. The coilexpander 2 usually falls off downwardly and hence, the constructionwhich forms the projecting portion 28 only on the lower portion of theinner-peripheral groove portion 26 also can prevent the coil expanderfrom falling off. Here, although the projecting portion is formed onlyon the lower portion of the peripheral groove portion 26 in the drawing,with respect to the oil ring body 1 served in an actual operation,usually, there is no distinction between the upper portion and the lowerportion and hence, the oil ring body 1 is mounted in a posture that aside of the oil ring body 1 where the projecting portion is formed isset as a lower side.

Further, even when the projecting portions are formed on both sides ofthe oil ring body 1, ΔL1 and ΔL2 are not always required to have thesame distance and the relationship between them may be set to ΔL1>ΔL2 orΔL1<ΔL2. As mentioned previously, usually, the coil expander 2 falls offtoward the lower side and hence, when the maximum value L2 is fixed, thelower projecting portion 28 is formed larger than the upper projectingportion 27. That is, by setting the relationship between them toΔL1<ΔL2, it can be effectively achieved to prevent the coil expander 2from falling off. Here, “upper” and “lower” correspond to “upper” and“lower” at the time of mounting the combined oil control ring.

By extending the radial thickness of the oil ring body 1 toward theinward direction thus increasing the radial thickness of theinner-peripheral protruding portions 15, 16, it is possible to preventthe coil expander from falling off. Although not shown in the drawing,by extending the radial thickness and by forming the projecting portionsin the inner peripheral groove, the falling-off prevention effect of thecoil expander can be further enhanced. However, when the radialthickness of the inner-peripheral protruding portions 15, 16 isincreased, there exists a tendency that the conformability of the oilring to the cylinder wall is lowered and hence, it is necessary todetermine the optimum radial thickness, that is, the optimum thicknessof the oil ring in view of both of these characteristics.

EXAMPLES 1 TO 6

A martensitic stainless steel wire having a cross section of oil ringbody shown in FIG. 1 is wound around to define a bore diameter thusproducing the oil ring body shown in FIG. 1. Here, a tension Ft of theoil ring is set to 10 N, a nominal diameter is set to 75.0 mm, a radialthickness of the ring body is set to 1.5 mm, and an axial width of thering body is set to 1.5 mm. While setting L2 at the largest portion ofthe inner peripheral groove space to L2=1.092 mm (BB′), the oil ringbodies which form the projecting portions 27, 28 in a vertical symmetryare manufactured such that inner peripheral groove space has the minimumdistances L1 shown in Table 1 at the open peripheries.

COMPARISON EXAMPLE

The oil rings shown in FIG. 4 are manufactured in the same manner as theexample 1. A tension of the oil ring, a nominal diameter, a radialdirectional thickness and an axial width of the ring body are set to thesame values as the example 1. In this specification, the projectingportions are not formed and hence, the axial width at the openperipheries 27, 28 is 1.092 mm and corresponds to the largest width L2(L1=L2) in the inner peripheral groove space. This conventional ring isused as a comparison example.

[Mounting Confirmation Test]

Coil expanders having a coil diameter d of 1.060 mm are inserted intothe oil ring body of the comparison example and the respective oil ringbodies of the examples 1 to 6. The mounting confirmation test isperformed on whether or not the coil expander falls off the oil ringbody in mounting the combined two-piece oil control ring on the piston.After assembling the oil ring body and the coil expander, using a abutends widening jig, an opening between but ends of the oil ring body iswidened to 16.5 mm which is 11 times as large as 1.5 mm which is theradial thickness of the oil ring body and, then, the oil ring is mountedin the oil ring groove of piston. It is judged whether the oil ring canbe mounted in the oil ring groove of the piston while preventing thecoil expander from falling off the oil ring body at the time of wideningthe opening between but ends of the oil ring body. The test is carriedout on 100 pieces of oil ring bodies with respect to each ringspecification and the number of the oil rings which the coil expanderfalls off is counted. The result of the test is shown in Table 1.

Compared to the comparison example in which the projecting portions arenot formed, in the examples in which the projecting portions are formed,the number of the oil rings which the coil expander falls off isdecreased. By forming the projecting portions such that a ratio of(L2−L1)/L1 assumes 0.03 or more, the remarkable falling-off preventioneffect of the coil expander is observed. On the other hand, when theratio of (L2−L1)/L1 exceeds 0.15, it is difficult to insert the coilexpander into the oil ring body. TABLE 1 Number of coil expander fallenL1 L2-L1 (L2-L1)/L1 off example 1 1.070 0.022 0.02 6 example 2 1.0600.033 0.03 1 example 3 1.038 0.054 0.05 0 example 4 0.989 0.103 0.10 0example 5 0.950 0.142 0.15 0 example 6 0.933 0.159 0.17 — comparison1.092 0 0 10  example

EXAMPLE 7

In the same manner as the example 1, the oil ring bodies in which atension Ft of the oil ring is set to 10 N, a nominal diameter is set to75.0 mm, a radial thickness of the ring body is set to 1.5 mm, and anaxial width of the ring body is set to 1.5 mm are produced. However, inthis example, L2 at the largest portion of the inner peripheral groovespace is set as L2=1.09 mm and L1 at the open peripheries is set toL1=1.01 mm. Further, the widths of the upper and lower projectingportions are made different from each other such that ΔL1 assumes 0.028mm and ΔL2 assumes 0.052 mm.

After combining the coil expander having a coil diameter d of 1.060 mmwith the obtained oil ring body, the mounting confirmation test isperformed in the same manner as the example 1 such that ΔL2 is disposedat the lower side. As a result, in 100 combined oil control ringstested, no falling off of the coil expander is recognized.

EXAMPLE 8

In the same manner as the example 1, the oil ring bodies shown in FIG. 3are produced. Here, however, L2 at the largest portion of the innerperipheral groove space is set as L2=1.12 mm and L1 at the openperipheries is set to L1=1.067 mm. Further, no projecting portion isformed on the upper portion of the oil ring body so that ΔL1 assumes 0mm and the projecting portion is formed only on the lower portion of theoil ring body, wherein ΔL2 assumes 0.028 mm. By combining the coilexpander having a coil diameter d of 1.060 mm with the obtained oil ringbody, the mounting confirmation test is performed in the same manner asthe example 1 in a state that the portion where the projecting portionis formed is set as a lower side. As a result, the number of coilexpander fallen off is two in 100 combined oil control rings tested.

EXAMPLES 9 TO 15

In the same manner as the example 1, the oil ring bodies in which atension Ft of the oil ring is set to 10 N, a nominal diameter is set to75.0 mm, a radial thickness of the ring body is set to 1.5 mm, an axialwidth of the ring body is set to 1.5 mm, and L1 takes values shown inTable 2 at the opening peripheries are produced. In these oil ringbodies, the projecting portions 27, 28 are formed in a verticalsymmetry. By combining the coil expander having a coil diameter d of1.055 mm with the obtained oil ring body, the mounting confirmation testis performed in the same manner as the example 1. The obtained result isshown in Table 2. When a value of L1−d is decreased to approximately 0.3mm, the remarkable falling-off prevention effect of the coil expander isrecognized. Although the falling-off prevention effect of the coilexpander is further enhanced by further decreasing the value of L1, whenthe value of L1−d assumes −0.20, it is impossible to insert the coilexpander into the oil ring body without causing the plastic deformation.TABLE 2 Number of coil L1 L1-d expander fallen off example 9 0.85 −0.205— example 10 0.95 −0.105 0 example 11 1.05 −0.005 0 example 12 1.150.095 1 example 13 1.25 0.195 2 example 14 1.35 0.295 2 example 15 1.450.395 6

EXAMPLE 16

The oil ring bodies shown in FIG. 1 are produced in the same manner asthe example 1. Here, however, the ends of the open peripheries areextended only in the radially inward direction and the thickness in theradial direction is set to 1.575 mm which is 5% thicker than L3 (1.5 mm)and, further, projecting portions are formed on the open peripheries ina vertical symmetry thus producing the oil ring body having L1 of 1.062mm. Further, as a comparison example, the oil ring body which has theradially extended thickness of 1.575 mm and has no projecting portionsis produced (comparison example 2). The coil expander having a coildiameter d of 1.060 mm is combined with the respective obtained oil ringbodies. The mounting confirmation test is performed in the same manneras the example 1. As a result, with respect to the comparison example 2,the number of coil expander fallen off is 7 in 100 combined oil controlrings tested, while with respect to the example 16, falling-off of thecoil expander is not recognized.

The explanation has been made with respect to a case in which the innerperipheral surfaces 18, 19 of the oil ring body which are portionsbrought into contact with the coil expander 2 have an arcuate shape.However, the substantially same advantageous effect can be obtained evenwhen the inner peripheral surfaces 18, 19 of the oil ring body whichconstruct coil-expander contact portions have a tapered shape (see FIG.2).

According to the present invention, in mounting the oil ring on thepiston by widening the opening between the but ends of the oil ring bodyof the combined oil control ring, it is possible to prevent the coilexpander from falling off the oil ring body and hence, the combined oilcontrol ring which enables the extremely easy assembly can be realized.

1. A combined oil control ring consists of: an oil ring body which isintegrally formed of upper and lower rails which bring outer peripheralsurfaces thereof into slide contact with an inner surface of a cylinderand a web which connects the upper and lower rails and includes aplurality of windows, and a coil expander which pushes the oil ring bodyin the direction toward the inner surface of the cylinder, the coilexpander being housed in an inner-peripheral groove of the oil ringbody, wherein projecting portions which extend toward a center line inthe thickness direction are formed at inner peripheral sides in theradial direction than a position where an axial distance between innerperipheries of the inner-peripheral groove portion of the oil ring bodybecomes maximum.
 2. A combined oil control ring according to claim 1,wherein the axial distance between inner-peripheries of theinner-peripheral groove portion of the oil ring body smaller than themaximum distance L2, in the inner portion than the position of L2.
 3. Acombined oil control ring according to claim 2, wherein the minimumdistance L1 and the maximum distance L2 satisfy a relationship of0.03≦(L2−L1)/L1≦0.15.
 4. A combined oil control ring according to claim1, wherein a cross-sectional shape in the radial direction of theinner-peripheral groove portion of the oil ring body is formed of anarcuate surface.
 5. A combined oil control ring according to claim 1,wherein a cross-sectional shape in the radial direction of theinner-peripheral groove portion of the oil ring body includes a pair ofinclined surface which face each other and a vertical surface in theaxial direction which connects both inclined surfaces.
 6. A combined oilcontrol ring according to claim 1, wherein the projecting portion isformed on only one periphery of the inner-peripheral groove portion ofthe oil ring body.
 7. A combined oil control ring according to claim 1,wherein the maximum widths in the axial direction of the projectingportions formed on upper and lower portions of the inner-peripheralgroove portion of the oil ring body differ from each other.
 8. Acombined oil control ring according to claim 2, wherein the minimumdistance L1 and an outer diameter d of the coil expander have arelationship of 0.2 mm ≧L1−d≧−1.10 mm.
 9. A combined oil control ringaccording to claim 1, wherein the projection portion is partially formedon the oil ring body in a circumferential direction.